Numerical simulation of flow-sediment dynamics in wave-current bottom boundary layer: II: sediment transport modelling

Numerical modelling of the bottom boundary layer (BBL) is an important tool for sediment transport analysis. In order to study the sediment movement in the wave-current BBL,an intra-wave process based 1DV model was established for silt-sand sediment concentration processes,considering the interactions among flow dynamics-sediment-bed forms. Some key approaches for silt-sand sediment are represented:the bed form module provides the type of bed form and related parameters;different approaches for sediment diffusivity over rippled beds and flat beds are employed;approaches for hindered settling velocity,reference concentration and critical shear stress for silt and sand are employed;the stratification effects and hindered settling are introduced to simulate interaction effects between flow dynamics and sediment concentration. A number of experimental datasets were collected to verify the model,and results showed that the model could properly simulate the sediment dynamics over different bed forms and in different combinations of wave-current conditions. Discussions are made on the simulation methods over different bed forms. The results showed that bed form is one of the important factors that impacts the sediment concentration profile,and it is not appropriate to simulate the concentration profile over a vortex rippled bed by only changing the roughness height and different approaches are suggested to be employed. This paper provides a tool for the study of the sediment transport in the wave-current BBL.